A successor communication system to W-CDMA and HSDPA, i.e., Long Term Evolution (LTE), is currently being discussed by 3GPP, a standardization group for W-CDMA. In LTE, orthogonal frequency division multiplexing (OFDM) is to be used as a downlink radio access method and single-carrier frequency division multiple access (SC-FDMA) is to be used as an uplink radio access method (see, for example, 3GPP TR 25.814 (V7.0.0), “Physical Layer Aspects for Evolved UTRA,” June 2006).
In OFDM, a frequency band is divided into multiple narrow frequency bands (subcarriers) and data are transmitted on the subcarriers. The subcarriers are densely arranged along the frequency axis such that they partly overlap each other but do not interfere with each other. This method enables high-speed transmission and improves frequency efficiency.
In SC-FDMA, a frequency band is divided into multiple frequency bands and the frequency bands are allocated to different terminals for transmission in order to reduce interference between the terminals. Also, SC-FDMA reduces variation of the transmission power and therefore makes it possible to reduce power consumption of terminals and to achieve wide coverage.
In uplink and downlink of LTE, one or more physical channels are shared by multiple user devices for communication. A channel shared by multiple mobile stations is generally called a shared channel. In LTE, a physical uplink shared channel (PUSCH) is used for uplink and a physical downlink shared channel (PDSCH) is used for downlink.
In a communication system employing shared channels, it is necessary to signal allocation information of the shared channels to user devices for each subframe (1 ms in LTE). In LTE, a control channel used to signal the allocation information is called a physical downlink control channel or a downlink (DL) L1/L2 control channel. The physical downlink control channel, for example, includes downlink (DL) scheduling information, acknowledgement information (ACK/NACK), an uplink (UL) scheduling grant, an overload indicator, and a transmission power control command bit (see, for example, R1-070103, Downlink L1/L2 Control Signaling Channel Structure Coding).
Meanwhile, broadcast channels include a first broadcast channel (primary broadcast channel (P-BCH)) and a dynamic broadcast channel (D-BCH).
The primary broadcast channel is transmitted using a fixed transmission method as in the case of a broadcast channel in W-CDMA. The primary broadcast channel is used to report minimum basic information. The dynamic broadcast channel is used to report information other than the information reported by the primary broadcast channel. The dynamic broadcast channel is transmitted via a shared data channel.
There is a consensus to transmit the primary broadcast channel at a cycle of “x” ms, and it has been proposed to set “x” at 40 (see, for example, R2-072183, System Information, May 2007). Also, there is a consensus to transmit the same control information “M” times within the cycle of “x” ms for transmitting the primary broadcast channel, and it has been proposed to set “M” at 2 or 4. Each transmission of the control information is called a burst.
For example, if the primary broadcast channel is to be transmitted four times in a cycle of 40 ms, it means that the primary broadcast channel is transmitted every 10 ms as shown in FIG. 1.